1. Field of the Invention
The present invention relates generally to cavity resonators and, more particularly, to coupling mechanisms for, and a filter using, TE.sub.01.delta. and TE.sub.011 mode resonators.
2. Description of the Related Art
In numerous electrical devices, such as electromagnetic filters, pairs of resonators are coupled together to pass electromagnetic energy from one resonator to the other resonator. The electromagnetic frequency response of individual resonators allows multiple resonators to be connected to create an electromagnetic filter having a desired frequency response. Currently, several different mechanisms are used to couple resonators. In one arrangement used for cylindrical TE.sub.011 and TE.sub.01.delta. mode resonators, each of the resonators has a slot in the longitudinal direction that exposes the internal cavity of the resonator to an external environment. The resonators are positioned in close proximity to each other with the slots aligned to couple magnetic fields within the resonators, thereby facilitating communication of the electromagnetic energy between the resonators.
In another arrangement, the resonators are connected by a conductive filament. The end portions of the filament form probes that extend into the inner cavities of the resonators. In this arrangement, the electromagnetic field in one resonator creates a current in the filament which, in turn, creates an electromagnetic field in the other resonator.
In coupling arrangements such as those described above, the coupling mechanism cannot be adjusted after assembly is complete. The electromagnetic field created in the second resonator may be out of phase with the electromagnetic field in the first resonator by a given amount which is determined by the characteristics of the coupling mechanism. This phase difference is constant regardless of the magnitude of the electromagnetic field in the first resonator. Additionally, the magnitude of the electromagnetic field in the second resonator is varied only by varying the magnitude of the electromagnetic field in the first resonator. In this way, the operation of the coupled resonators is set when the resonators are coupled together.
Therefore, there is a need for an improved coupling mechanism for TE.sub.011 and TE.sub.01.delta. resonators that provides an adjustable coupling between the resonators, and which allows adjustment of the magnitude and/or phase of the electromagnetic energy passed from the first resonator to the second resonator. A need also exists for improved coupling mechanisms that couple two resonators with waveguides to provide control of the relative coupling of the electromagnetic energy that is transferred between the waveguide and the coupled resonators.